1. Field of the Invention
This invention relates to a method for forming a spiral bevel gear, more particularly to a method and mold die for forming a spiral bevel gear from metal powders.
2. Description of the Related Art
To form a spiral gear, referring to FIG. 1, a conventional mold die 10 has a die cavity 111 that corresponds to a contour of the spiral gear. The die cavity 111 has a plurality of spiral threads 112 to correspond to the spiral teeth of the spiral gear. Upper and lower spiral gears 12,13 have spiral teeth 121,131 which conform to the spiral teeth of the spiral gear. After filling the die cavity 111 with metal powders, the upper and lower spiral gears 12, 13 are screwed from the top and bottom of the die cavity 111 so as to form a green compact 14.
Therefore, after the upper spiral gear 12 is screwed out of the die cavity 111, the lower spiral gear 13 is screwed gradually upward so as to eject the green compact 14 out of the die cavity 111 by the threaded rotation of the green compact 14 in view of the threaded engagement between its spiral teeth and the spiral threads 112 of the die cavity 111.
However, the method described above and the mold die 11 are not suitable for forming a spiral bevel gear because the spiral bevel gear has different diameters and is difficult to be removed from the die cavity of such mold die. An additional machining process, such as a thread milling process, is required to form the spiral teeth of the spiral bevel gear, thereby resulting in inconvenience during manufacturing and adversely affecting the quality of products.